débris. The insects themselves will give an answer to the question if several of them are placed in glass tubes and covered with earth; but, to understand the cicada's technique, we must first study the mechanism of its digging tools, the front legs.
The front leg of a mature cicada nymph (Fig. 116 A) is
Fig. 116. The digging organ, or front leg, of the mature cicada nymph.
A, right leg, inner surface (4 times natural size.) B, the tarsus (Tar) bent inward at right angles to the tibia (Tb), the position in which it is used as a rake
Cx, basal joint or coxa; Tr, trochanter; F, femur; Tb, tibia; Tar, tarsus, with two terminal claws
composed of the same parts as any other of its legs. The third segment from the base, which is the femur (F), is large and swollen, and has a pair of strong spines and a comb of smaller ones projecting from its lower edge. The next segment is the tibia (Tb). It is curved and terminates in a strong recurved point (B). Finally, attached to the inner surface of tibia, well up from its terminal point, is the slender tarsus (Tar). The tarsus can be extended beyond the tibial point when the insect is walking or climbing, but can also be turned inward at a right angle to the latter, as shown at B, or bent back against the inner surface of the tibia.
Let us now return to the insects in the earth-filled tubes, where they are industriously at work. It will be seen that they are using the curved, sharp-pointed tibiae as picks with which to loosen the earth, the tarsi being turned back and out of the way. The two legs, working alternately, soon accumulate a small mass of loosened material in front of the insect's body. Now there is a
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